This invention concerns the provision of clamp-on ultrasonic flowmeters.
Such ultrasonic flowmeters, as is well known, are secured to the outside of a pipe, particularly of a pipe already permanently installed within a pipe system, without the need for any modification af the pipe, e.g., for making a hole-therein. They also require no specially prepared measuring tube as is necessary in flowmeters based on other measuring principles, such as in vortex flowmeters, electromagnetic flowmeters, or Coriolis mass flowmeters.
U.S. Pat. No. 3,869,915 describes a clamp-on ultrasonic flowmeter with a sensor assembly comprising two sensors which are spaced along a straight surface line of a pipe conducting a fluid to be measured and are secured to the pipe by means of first and second pipe straps, respectively.
In the single FIGURE of U.S. Pat. No. 4,738,737, but not in the pertinent description, a clamp-on ultrasonic flowmeter is disclosed comprising a first sensor assembly and a second sensor assembly,
the first being attached on a first straight surface line of a pipe by means of first and second pipe straps, and the second being attached at a given distance from the first on a second straight surface line essentially opposite to the first straight surface line by means of third and fourth pipe straps,
the two sensor assemblies being identical in construction.
The last-mentioned U.S. Patent does not describe how the two sensor assemblies, if they are located on opposite straight surface lines, were aligned with respect to each other or how the two sensor assemblies have to be positioned at a distance from each other along a single straight surface line.
It is an object of the invention to provide an improved clamp-on ultrasonic flowmeter comprising two sensor assemblies which is usable for different nominal diameters of pipes and can be positioned either along a single straight surface line or along diametrically opposed straight surface lines.
Furthermore, the clamp-on ultrasonic flowmeter is to be so designed that it contains replaceable components, so that in the event of a malfunction, only faulty components need to be replaced.
To attain these objects, the invention provides a clamp-on ultrasonic flowmeter comprising a first sensor assembly and a second sensor assembly
which are positioned at a given distance from each other
either along one straight surface line of a pipe conducting a fluid to be measured
or along a first straight surface line of the pipe and a diametrically opposed, second straight surface line, respectively, and
attached by means of a first pipe strap and a second pipe strap, respectively, and
which are identical in construction and each comprise:
a flat bracket adjacent to the pipe and having a longitudinal center line and a tubular portion integrally formed thereon;
a sensor inset longitudinally guided in the tubular portion and containing an ultrasonic transducer with a transducer element;
a sensor cap which is put over the tubular portion, is secured to the tubular portion by means of a snap fastening releasable by rotation, and comprises a spring which forces the sensor inset against the pipe; and
a strap-tightening device fixed in the bracket approximately in the middle of the longitudinal center axis thereof and having an axis.
In a first preferred embodiment of the invention, the sensor inset ends in a cable pipe, and the sensor cap is rotatably mounted on the cable pipe.
In a second preferred embodiment of the invention, which can also be used with the first preferred embodiment, the strap-tightening device comprises:
a spiral spring;
a spring housing mounted in the bracket on the longitudinal center axis thereof by means of a threaded neck having a central hole;
a tightener having a first end serving as a strap guide through which the strap runs, and a second end designed as a threaded stud; and
a nut rotatable in the spring housing and screwed onto the threaded stud for tightening the strap.
In a third preferred embodiment of the invention, which can also be used with the first or second preferred embodiment, at least one series circuit consisting of an air-core coil and at least one resistor is disposed within the sensor inset near the ultrasonic transducer, and is connected in parallel with the transducer element.
An essential advantage of the invention is that it provides a clamp-on ultrasonic flowmeter which meets all assembly, adjustment, and repair requirements.